There's also some really nice profiling data at #1818266: [meta] A secure theme system (with twig), but that deals with the auto-escape system and this issue's about more "raw" data just in template/theme function conversions before we start adding in more doo-dads.

What is important is to no longer test against the base overhead of Twig itself (that was fine according to all involved), but to the overhead when twig is already loaded to isolate things.

Of course we can also again test the "raw" overhead, but that is dependent on class loading, etc.

That means compare:

* one node in core (rendered via twig) and 200 calls to views-view-field.tpl.php

with

* one node in core (rendered via twig) and 200 calls to views-view-field.html.twig

Also make sure to activate APC and APC class loader.

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Shameless plug: And make sure to checkout https://github.com/LionsAd/xhprof-kit for easy branch testing, which allows to upload run data for all others to see and such full disclosure of tested things.